Seismic surveying is a method for determining the structure of subterranean formations in the earth. Seismic surveying can utilize seismic energy sources that generate seismic waves, and seismic receivers that are positioned to detect the seismic waves. The seismic waves propagate into the formations in the earth, where a portion of the waves reflects from interfaces between subterranean formations. The reflected seismic waves are detected by the seismic receivers, which convert the reflected waves into representative seismic datasets. The datasets can be transmitted by electrical, optical, radio or other techniques to devices which record the datasets. Through analysis of the recorded datasets, the shape, position and composition of subterranean formations can be determined.
Land seismic surveying is a method for determining the structure of subterranean formations beneath the surface of the earth. Seismic sources and seismic receivers for land seismic surveying can be placed on the surface of the earth. In different examples, the seismic source(s) or seismic receiver(s), or both, may be placed in a borehole for vertical seismic profiling.
Marine seismic surveying is a method for determining the structure of subterranean formations underlying bodies of water. Marine seismic surveying can utilize seismic energy sources and seismic receivers located in the water and can be towed behind a vessel or positioned on the water bottom from a vessel. Marine seismic surveying can also employ seismic receivers deployed on a seabed cable. The energy source is typically an explosive device or compressed air system which generates seismic energy, which then propagates as seismic waves through the body of water and into the earth formations below seabed. As the seismic waves strike interfaces between subterranean formations, a portion of the seismic waves reflects back through the earth and water to the seismic receivers, to be detected, transmitted, and recorded. The seismic receivers typically used in marine seismic surveying are pressure sensors, such as hydrophones. Additionally, though, motion sensors, such as accelerometers may be used. Both the sources and receivers may be strategically repositioned to cover the survey area.
Seismic waves, however, reflect from interfaces other than just those between subterranean formations, as would be desired. Seismic waves also reflect from the water bottom and the water surface, and the resulting reflected waves themselves continue to reflect. Waves which reflect multiple times are called “multiples”. Waves which reflect multiple times in the water layer between the water surface above and the water bottom below are called “water-bottom multiples”. Water-bottom multiples have long been recognized as a problem in marine seismic processing and interpretation, so multiple attenuation methods based on the wave equation have been developed to handle water-bottom multiples.
In marine seismic surveying, seismic waves do not reflect just from the interfaces between subterranean formations. Seismic waves also reflect from the water bottom (e.g., seafloor) and the water surface (e.g., sea surface), and the resulting reflected waves themselves continue to reflect. Waves that reflect multiple times are called “multiples.” The presence of multiples data in recorded seismic data can adversely affect the accuracy of assumptions made during seismic processing and resulting interpretations made using interpretation techniques.